1. Field of the Invention
This invention relates to a blade for electrophotographic apparatus which is used in electrophotographic apparatus.
2. Related Background Art
In general, electrophotographic apparatus are provided with various blades such as a cleaning blade for removing a toner remaining on a photosensitive member after developer images have been transferred to a recording sheet and a developing blade which forms a toner thin layer while triboelectrically charging a toner held on a developing sleeve in a developing assembly. These blades are usually constituted of a support and joined thereto a blade member formed using an elastic member.
The cleaning blade is manufactured in such a way that the blade member prepared using an elastic member is set integral to a leaf edge portion of a support member such as a holder made of a metal; the holder being used to attach the cleaning blade to an electrophotographic apparatus. As the blade member, one formed using a polyurethane resin is usually used because of its superior wear resistance and compression set.
The polyurethane resin is produced by a prepolymer method, a semi-one-shot method or a one-shot method, using a polyisocyanate, a polyol, a chain extender and a catalyst.
For example, where the blade member is manufactured by the prepolymer method, it is manufactured by preparing a prepolymer by using a polyisocyanate and a polyol, adding the chain extender and the catalyst to the prepolymer, and thereafter casting the resultant material into a mold for molding, followed by curing. The time taken after the material is casted into the mold and until it is cured and released from the mold, i.e., the curing time influences manufacturing efficiency greatly. If the curing time is long, the mold must be made ready in a large number, and this requires an enormous investment. Accordingly, studies are made in variety so as to shorten the curing time.
In an attempt to shorten the curing time by enlarging the quantity of a catalyst, using a catalyst capable of accelerating urethanation as exemplified by triethylenediamine or dimethylimidazole, conventionally used in general purposes, the curing reaction takes place faster immediately after mixing of the catalyst, with an increase of the catalyst, to make the liquid material highly viscous. Hence, the liquid material does not spread throughout the mold, resulting in an insufficient flowability. Also, the liquid material may cure in a mixing chamber of a molding machine and may be casted in the state a urethane sediment has mixed in the liquid material, to cause a problem that foreign matters mix in the molded product.
Accordingly, to solve these problems, a highly temperature-sensitive isocyanurating catalyst is often used which little shows its activity until the liquid temperature reaches a stated temperature, and makes the curing reaction proceed rapidly after the liquid temperature has become higher than the stated temperature (see, e.g., Japanese Patent Application Laid-open No. H08-281837).
The use of the isocyanurating catalyst brings an improvement in flowability to mold. However, when cured, if a polyol having a number average molecular weight of 1,500 to 3,000 and a chain extender having a molecular weight of 300 or less are used in combination, the reaction tends to come non-uniform because of a too great difference in molecular weight between them. Also, since the reaction proceeds rapidly at a stated temperature or more, the reaction tends to come non-uniform, so that the molded product may come strained or a surface pattern may be caused by the non-uniformity of shrinkage. There have been such problems.